Visual displays (e.g., televisions and monitors) are designed and implemented using many different approaches. Cathode ray-tube displays have been in use for some time. The thickness of a conventional cathode ray tube television set is dependent upon the length of the cathode ray tube and the cathode ray tube length generally increases in proportion to the display size of the television. Increasingly, such displays are designed with greater displayable area and decreased thickness. Often, decreasing the thickness of the displays increases the difficulty of providing sufficient power and of removing excess heat from the display.
Some relatively newer visual display types are implemented using a light generator and a light attenuating arrangement. The attenuating arrangement varies from system to system. The attenuation is often accomplished by varying the amount of light absorbed and/or redirected prior to the light reaching a viewable portion of the display. These types of attenuating displays do not use cathode ray tubes, and therefore, can often be thinner than a conventional cathode ray tube television.
A specific example of an attenuating display is a liquid crystal display (LCD). Conventional LCD displays are designed with a single light generating element (a backlight) that operates at a constant brightness level. The power dissipation of conventional backlights is linked to the peak brightness for which the display is designed, and darker images require severe attenuation by the LCD front panel to remove the excess light produced, further increasing power consumption.
Another type of attenuating display is a display employing Digital Light Processing™ (DLP®) technology, in which small mirrors on at least one microchip selectively direct light towards or away from a display. Digital Light Processing™ technology and DLP® technology are registered trademarks of Texas Instruments, Inc. Attenuation is achieved via the amount of light directed towards, relative to away from, the display.
Some example LCD displays implement light generating and light attenuating elements in a sandwiched way. For a projection type display (e.g., with DLP or LCOS light attenuators), the light attenuating and the light generating elements are part of a complex optical path. In the first case the image is directly viewable, in the latter case it is projected onto a screen material for indirect view.
Attenuation type displays have become a ubiquitous electronics component, from large high-brightness home entertainment displays to small battery-operated mobile displays. Regardless of size or application, power dissipation is a key limiting factor of display performance. In the case of large displays, size and brightness levels are primarily limited by power dissipation and cooling. For example, more than 1 kW are required to achieve 2000 cd/m2 on a 30″ LCD given an efficient fluorescent backlight. While larger sizes and higher brightness are desirable, the power-dissipation by itself, and additionally the cooling technology that would be needed, impede the development of such products with reasonable weight, price, or fan-noise levels. Power consumption is also critical for small, battery-operated, mobile LCD displays. The power consumption associated with the display is a large fraction of the total energy dissipated by mobile devices, often exceeding 50%. Thus, a significant reduction in display power consumption is essential for the continued successful development of mobile devices, enabling a reduction in battery size, and hence, device size, or making possible a substantially longer battery runtime.
These and other characteristics present challenges to the implementation of attenuating displays.